[Roler]

It's been a while, and so it was for the XJ
Had been sitting a few months, charged the battery, did some pre-start fuel conditioning and started up fine.

As the engine was idling, did some testing in the engine bay and noticed by battery voltage being below 12.4.
Putting increased load on it, made it even go to 12V. Jeep kept running pretty much the same during this.
Increasing the rpm's would bring it up to 13.8 Volts, what it has always done (never has charged over 13.9 in the past 12 years, even with the previous alt in there) . Letting it idle back down would drop the batt voltage again to below starting voltage.

It is a 2nd-hand alternator from the junkyard, about 2 years ago.

- Cleaned up all the grounds, including the 2 on the coilmount.
- Did a load test on the battery, reading remained within good range.

- Did voltage drop test: No voltage drop over the positive or negative side between alt and battery
(about 0.006V)

- B-terminal showed batt voltage with engine running idle and with increased rpm's.

- Gave the alt a few loving taps, in case it would " free up" something.



So in short: it doesn't charge the battery at idle, but seems to be able to put out enough when raising the rpm's


I think the voltage regulation ( from the ECU) could possibly at fault, but this would be less likely as I understand from reading up. It would mean that only at idle the ECU doesn't tell the alt to start charging, which I think would be unlikely (but its a Jeep)

Alternator the cause?

Anything else I could or should check?

Cheers